Field of the Invention
The present invention relates to a fuel cell system and a method for controlling the same, and more particularly to a fuel cell system and a method for controlling the same which rapidly increases a temperature of a fuel cell stack under cold start conditions.
Description of the Related Art
A fuel cell vehicle includes a fuel cell stack in which a plurality of fuel cells used as a driving power source are stacked, a fuel feeding system configured to feed hydrogen, that operates as a fuel, to the fuel cell stack, an air feeding system configured to feed air, which is used as an oxidizing agent in an electrochemical reaction in the fuel cell stack, and a heat-and-water management system configured to adjust a temperature of the fuel cell stack.
The fuel feeding system reduces a pressure of compressed hydrogen stored in a hydrogen tank and supplies the pressure-reduced hydrogen to a fuel electrode (anode) of the fuel cell stack. The air feeding system is also configured to operate a blower to supply suctioned air to an air electrode (cathode) of the fuel cell stack.
When hydrogen and oxygen are supplied to the fuel electrode and the air electrode of the fuel cell stack, respectively, hydrogen ions are produced from the fuel electrode through a catalytic reaction. The produced hydrogen ions move to an oxidation electrode (air electrode) through an electrolyte membrane, and electrochemical reactions occur among the hydrogen ions, electrons, and oxygen, thus producing energy. More specifically, an oxidation reaction occurs through an electrochemical oxidation reaction of hydrogen in the fuel electrode, and a reduction reaction occurs through an electrochemical reaction of oxygen in the air reaction. Further, produced electrons move, thus producing electricity and heat. During this process, vapor or water is produced through a chemical reaction where hydrogen and oxygen are combined.
A discharging device is installed to discharge byproducts such as heat, vapor and water, which are produced while the fuel cell stack is generating electric energy, and remnants, such as hydrogen and oxygen. Gases such as vapor, hydrogen, and oxygen are released via a ventilating pipe. A current command issued by a current command generator is output to a current controller (not shown). The current controller is configured to generate a d-axis voltage command and a q-axis voltage command and then generate three phases of voltage commands. Therefore, a motor may be controlled through pulse width modulation and the three-phase current control.
When a fuel cell vehicle stops, a portion of water produced during driving of the vehicle remains within the fuel cell stack. When the exterior temperature is substantially low (e.g., below a predetermined temperature) the remaining water typically freezes and may eventually become ice and disable the start of an engine. There are various reliable methods of enabling a cold start. One method includes quickly thawing cooling water using a heater and another method includes heating air using a heater installed on a pipeline of an air feeding system.
However installing a heater on a suction pipeline disposed between an air blower and a humidifier at the time of cold starting and heating a fuel cell stack by ventilating an enclosure which surrounds the fuel cell stack using hot air discharged from the fuel cell stack have some disadvantages. Some examples of disadvantages are an additional heater is necessary to heat the fuel cell stack and the fuel cell stack requires a structural change. In other words, the necessary changes complicate the arrangement and design of constituent parts and increase the manufacturing cost. Furthermore, heating the fuel cell stack to a desired level using the heater requires a substantial increase in time.
The foregoing is intended merely to aid in the understanding of the background of the present invention, and is not intended to mean that the present invention falls within the purview of the related art that is already known to those skilled in the art.